Blasting device



R. J. MILLER ET AL BLASTING DEVICE Filed July 21, 1958 Feb. 20, I962 JET5.1

INVENTORS ROSS JAY MILLER GEORGE ADELBERT NODDIN ATTORNEY .detonatingfuse leading to the explosive charge.

3,021,786 BLASTING DEVICE Ross Jay Miller, Pittman, and George AdelhertNoddin, Seweil, N.J., assignors to E. I. du Pont de Nemours and Company,Wilmington, DeL, a corporation of Delaware Filed July 21, 1958, Ser. No.749,848 3 Claims. ((21. 10227) The present invention relates to a noveldelay initiator. More particularly, the present invention provides anonelectr'ic initiator and assembly including such initiator. Thisapplication is a continuation-in-part of the copending applicationSerial Number 619,991 filed on November 2, 1956, and now abandoned.

The art of delay blasting has been practiced for many years. In theearlier times, the primary purpose of providing an interval between theinitiation of the main explosive charges was to permit burden loosenedby each preceding blast to clear before the following blast occurred. Incertain cases, the delay between shots also permitted a count toascertain whether or not all shots had actually fired. For the foregoingpurposes, delay intervals of from /2 to several seconds were desired andused. .In more recent years, delay shooting to reduce ground vibrationand to improvefragmentation has been widely practiced. For this purpose,delay intervals of from 5 to 100 milliseconds are desired and used. Arelatively'high degree of accuracy is required for millisecond delayblasting, since a slow or undesirably fast initiation of one charge willprevent the desired vibration reduction and may have a deleteriouseffect on the fragmentation. For the longer interval delays, closeprecision is less important. a

Three means have been used in the past to achieve the desired delayedinitiation of the explosive charges. The

first known means involved a mechanical arrangement for controlling theapplication of electrical energy to the individual" electric blastingcaps. This means, with many refinements, is in use at the present time,particularly for millisecond delay shooting, and provides excellentaccuracy of timing and a relatively good selection of timing intervals.The next means developed was a delay electric blasting cap in which thedelay interval was provided by a delay train interposed between theelectrically-ignited charge and the detonating charge of the cap. Thismeans is widely used at present, both for long-period delaysand formillisecond delays. The most recent means developed is theinterpositioning' of a delay connector in a line of This means has beenapplied only to millisecond delay blasting and has become increasinglyaccepted for above-ground blasting. I

All of the foregoing procedures and assemblies have their advantages anddisadvantages. The chief advantage of the delay electric blasting cap isthat the delay interval is produced in the immediate vicinity of thecharge. In a shot in which a number of charges are fired in apredetermined sequence by means of delay electric blasting caps, asingle electrical impulse will initiate all of the caps. Thus, no dangerexists that ground movement or fragment throw from an earlier detonationmight prevent ignition of a. subsequent charge by severing orshortcircuiting the line leading to the subsequent charge. On the otherhand, the electric delay blasting cap is subject to the disadvantage ofall electric initiation devices, i.e., complicated electrical circuitsand the ever-present danger of accidental ignition by extraneouselectricity, i.e., electricity from a source other than the firingdevice. It is because of the hazards inevitable with direct electricinitiation of the explosive charges that detonating fuse has gained wideacceptance for above-'ground-blasting. Deto- 3,02i,78 Patented Feb. 20,1962 nating fuse lines are simple to connect and are free from thehazard of accidental initiation. However, the brisance of the detonatingfuse is such that the delay connector must be positioned a distance froma cap-sensitive explosive charge to avoid having the charge initiated bythe detonating fuse prior to the delay. Even if this distance is onlysmall, the danger of cut-off due to ground movement or fragments from anearlier detonation cannot be eliminated. Such cut-off results in failureto initiate the charge, thus disrupting the entire pattern and leavingan unexploded charge in the blasted area. Detonating fuse cannot be usedfor bottom hole priming of cap-sensitive explosive charges, a proceduregaining increased acceptance in present day blasting.

7 Delay blasting using a mechanical timing device is subject to both thedanger of accidental ignition of the electrical initiators by extraneouselectricity and to cutoff from previous blasts, since the electricalfiring impulse does not go to a later initiator until the previouscharge has been fired. f

Thus, a need has long existed for a delay blasting means wherein thedelay interval occurs in the immediate vicinity of the explosive chargeand which is not susceptible to accidental initiation; in other words, anon-electric delay device and assembly which can be positioned incontact with the explosive charge. 7 Accordingly, an object of thepresent invention is to provide such a delay device and assembly. Afurther object is to provide a delay device of high accuracy. A stillfurtherobject is to provide an assembly suitable for use for bottom-holepriming of explosive charges. Other objects will become apparent as thisinvention is more fully described.

The foregoing objects are achieved by providing a delay initiator whichcan be actuated by means of low energy connecting cord of the typedescribed and claimed in copending application Serial No. 744,586 filedJune 25, 1958, by D. J. Andrew, R. W. Felch, and-G. A. Noddin, nowPatent Number 2,982,210, and assigned to the present assignee. prises acentral continuous core of a high-velocity detonating' explosive encasedin a metal sheath, the core containing less than 10 grains of theexplosive per foot of length. Preferably, the metal, sheath will becountered with a fabrie orsynthetic polymeric material nitroglycerindynamite charge even when taped lengthwise to the cartridge.

Thus, the present invention includes a delay initiator adapted to beinitiated by the described low-energy connectingcord wherein none of thecharges except the priming and/or base load will initiate acap-sensitive explosive composition, and also an assembly of the delayinitiator and a length of low-energy connecting cord containing from 0.5to 2 grains of explosive per foot of length.

In order to more fully describe the present invention, reference now ismade to the accompanying drawings which are illustrative only, theinvention not being limited thereto. Each of the figures depictsmodifications of the basic assembly. Throughout the figures, the samenumber has been used to indicate the equivalent part of the element.

The low-energy connecting cord comsembly illustrated in FIGURE 1.

Referring now to the figures, and particularly FIG- URE 1, 1 representsa tubular shell having one integrally closed end, 2 represents a. basecharge of a detonating explosive, 3 represents a primer charge of aheat-sensitive detonating explosive, 4 represents an exothermicburningcomposition, 5 represents an openended metal capsule having a centralaperture 6, 7 represents an air gap, .8 represents the terminal end of alength of lowenergy connecting cord which is held in place by peripheralcrimps 9. In this figure, the connecting cord 8 isshown in partialsection, showing the explosive core 10., the metal sheath 11, and thecountering 12.. The assembly depicted in FIGURE 2 is identical to that,of FIGURE 1 except that a delay carrier 13 containing a delaycomposition 14 is interposed between the primer 3 and theexothermic-burning composition 4. The initiator illustrated in FIGURE 1can be designed to provide a precise delay periodof from 1 to 1.000milliseconds, depending on the depth of the exothermic-burningcomposition 4. In operation, the sequence is as follows forthisassembly. The initiating impulse from the detonation of theexplosive core jumps the air gap 7 enclosed by the capsule 5, passesthrough the aperture 6, and ignites the exothermic-burning composition4. This composition burns at a constant rate, and when thehot frontreaches the. priming charge 3, the latter is ignited. The primingcharge, in turn, initiates the base charge 2. The initiator depicted inFIGURE 2 provides a longer delay, i.e. 1-20 seconds, than that providedby the as- The sequence of operation of the modification illustrated inFIGURE 2 is identical to that described for FIGURE 1 except that theexothermic-burningcomposition 4 ignites the slow-burning' train of,delay composition 14, This delay composi tion 14, in turn ignites theprimer 3.

In order to illustrate our invention further, reference now. is made tothe, following examples.

EXAMPLE 1 A delay initiator was prepared utilizing an. aluminum shell1.03 inch in length, 0.277 inch in outside. diameter, and having a0.010-inch wall thickness. As abase charge, 7.2 grains of PETN was:charged to the shell and corn pacted at 200 pounds by a pointed pin. Ontop of this charge, 3.0 grains of lead azide, as. the primer, was loadedand compacted at the-same pressure as the base charge by a flat pin. Theexothermic-burning composition, 3.0 grains of a 2/98 mixture ofboron/red lead, grained with neoprene, was charged to the. shell and.compacted at 200 pounds by a dimpled pin. The dimpled pin consisted of aconventional solid cylinder designed to fit snugly into the aluminumshell and, at: the end which, was inserted adjacent to the base charge,a second cylinder 0.047 inch long and 0.114 inch indiameter. centrallypositioned and protruding from the first cylinder. An open-endedaluminum capsule 0.187 inch long and having a central apertureOLOStI-inch, in: diameter was inserted on top of the, exothermicrburningcomposition with the open end directed away from the loaded charges.

When this initiator was .tested, a low-energy connecting cord having 1grain of PETN per: foot of length was inserted into the assembledinitiator until it reached the capsule, thus leaving an air gap of 0.187inch between the end of the. cord and the exothermic-burningcomposition. When fired, the initiator gave a delay period of 9.9milliseconds.

EXAMPLE 2 Delay initiators were assembled as described in Example 1'except that the amount, percentage composition, and compacted shape ofthe exothermic-burning composition were varied. The delay periodsobtained when firing these initiators are reported in Table I.

Table I Boron-Red Lead Mixture Shape of Dcluv Compacting Period Amount(gr.) Percent Pin (ms Composition EXAMPLE 3 A long-period delayinitiator was assembled in an aluminurn shell having essentially thesame dimensions as the shell discussed in Example 1 except that a longerlength was required in order to accommodate the charges. PETN and leadazide, as the base and priming charge, respectively, were loaded andcompacted as described in Example 1. A delay carrier having a length of0.25 inch and a shell' wall thickness of 0.063 inch and containing acentral core of an /15 barium peroxide/selenium mixture, as aslowburning delay composition, wasplaced adjacent to the primer; of theexothermic-burning mixture identical to that described in Example 1 wasloaded and compacted at 200 pounds by a Hat pin. The open-ended aluminumcapsule was inserted as previously exemplified.

When the assembled initiator was tested, low-energy connecting cordcontaining 1 grain of PETN per foot of length was inserted into theloaded shell until it reached the aluminum capsule. Upon being tired,the initiator gave a delay period of 1.40 seconds.

scribed in Example 3 varying only the length of the delaycarrier. The.delay periods obtained on firing these initiators are reported in TableII.

Table Il Delay Delay Train Length (in.) Test Conditions IZeriogi Theparticular compositions selected for the various charges are notcritical to the present invention, provided 1that the selectedcompositions function as desired; Thus,

for the base charge, any of the usual base charge compositions may beused, e.g., RDX, lead azide, PETN, nitromannite, TNT, or HMX. As thepriming charge, heatsensitive detonating compositions such as leadazide, diazodinitrophenol, or mercury fulminate may be used. Obviously,when the priming composition and the base charge are identical, only oneload is required; For the exothermic-burning composition, anexothermic-reacting mix* ture of a metal and an oxidizing agent such asis com monly used in ventless delay initiatorsis preferred, e.g.,boron-red lead,magnesium/barium peroxide/cement, or silicon-red lead.For the long-period delay initiators, the delay composition contained inthe delay carrier may be any conventional gasless delay compositionwhich burns On top ohthecarrier, 1 grain bowaxes, are also suitable.

charges is varied depending on the effect desired. The composition ofthe rigid tubing surrounding the charges or spacing the charges also isnot critical, butlead or any pressure which is sufficient to retain thecharges in.

the shell. and not sufficient to cause desensitization of the charges issuitable.

The pressure and shape of the pin used for the cornpaction of theexothermic-burning composition is not;

critical to the ability of the initiator to function. However, the delayperiod is dependent upon the depth of the delay charge and amount ofcompaction of the exothermic-burning composition. Thereby, changes inthese variables from those illustrated will produce a change in thedelay period. The limits of pressure utilized to compact this charge areidentical to the limits of pressure for the base and priming charge,i.e., sufficient pressure to retain the composition in the shell and notdesensitize the charge. 1

As illustrated in the examples, the exothermic-burning compositionpreferably is grained prior to use, as exemplified by the treatment ofthe boron-red lead composition with neoprene. It is to be understood,however, that graining agents known in the art, such as solutions ofgum, shellac, polyethylene glycol, .Thiokol, and car- Although agraining agent usually is desired to facilitate loading, the presence orabsence thereof is not critical to the functioning of the device.

In the preferred embodiment of our invention, the open-ended metalcapsule enclosing an air gap and having a central aperture is positionedwith the open end directed away from the loaded charges. Thispositioning 2-inch length, one hundred percent performance was obtainedon testing the initiators of the present invention. Obviously, thisallowable variance is an asset in the use of the initiators in thefield.

Thus, the initiator of the present invention for use with a'low-energyconnecting cord having an explosive core of from 0.5 to 2 grains ofexplosive per foot of length, hasically comprises a tubular shell closedat one end and containing in order starting at the closed end, a basecharge, a priming charge, a delay-ignition composition, and an openendedmetal capsule. For a longer delay period, ie 1-20 seconds, a delay trainwithin a rigid tube is interposed between the delay-ignition compositionand the primer. Many modifications, other than those herein described,will be apparent to those skilled in the art. Therefore, the inventionis limited only by the following claims.

We claim: g

l. A non-electric delay initiator in combination with and adapted to beinitiated by a low energy connecting cord having an explosive core offrom 0.5 to 2 grains per foot of length comprising a rigid tubular shellintegrally closed at one end and containing in sequence a base charge"of a detonating explosive at said closed end, a priming is recommendedbecause the rounded corners of the capsule thus inserted serve to retainthe adjacent exothermicburning composition. However, if desired, thecapsule may be positioned in the reverse manner, i.e., so that the openend is directed toward the charges. Varying the diameter of the aperturein the capsule does not interfere with the functioning of the initiator.The functioning of an initiator in which a sleeve, i.e., a capsulehaving the maximum aperture diameter, is substituted for the preferredcapsule which has partial lower closure, is within the scope of thisinvention. An aperture is present in the capsule in order to permit easytransmission of the initiating impulse from the detonation of theconnecting cord to the delay composition. Thus, as long as there is anopening in the capsule, this condition will be satisfied.

The depth of the capsule may be varied. In addition,

the low-energy connecting cord may be inserted in the device until itreaches the bottom of capsule'or may be spaced away from the bottom ofthe capsule provided that the distance from the end of the cord to thedelay composition does not exceed 0.57 inch. A greater separationresults in unreliable functioning of the device. Within this range,however, contact up to 0.57 inch, which is considerable in shellsgenerally having less than a charge of a heat-sensitive detonatingexplosive, a delay charge of an exothermic-burning composition and atubular capsule positioned axially within the said shell contiguoustothe said delay charge, said capsule having a closure at one extremityprovided with a central orifice therethrough and one, open extremitypositioned in abutting relationship with said connecting cord.

2. The delay initiator of claim 1 wherein a delay carrier comprising atube of rigid material containing a central core of a gasless delaycomposition is interposed between the said priming charge and the saiddelay composition.

3. An initiator delay assembly comprising a rigid tubular shellintegrally closed at one end and containing in sequence a base charge ofa detonating explosive at the closed end of said shell, a priming chargeof a heatsensitive detonating explosive, a delay charge of anexothermic-burning composition, a tubular capsule positioned axiallywithin the said shell contiguous to the said delay charge, said capsulehaving a closure at one extremity provided with a central orificetherethrough and one open extremity, and a length of low energycontinuous connecting cord positioned in abutting relationship with theopen extremity of saidcapsule, said cord comprising a central core offrom 0.5 to 2 grains of high velocity detonating explosive per foot oflength and a metal sheath encasing the said core.

References Cited in the file of this patent UNITED STATES PATENTS Re.20,190 Lewis Dec. 1, 1936 868,876 Lheure Oct. 22, 1907 882,154 1 LheureMar. 17, 1908 2,360,698 Lyte Oct. 17, 1944 2,402,235 Burrows June 18,1946 2,424,374 Taylor July 22, 1947 2,475.875 Burrows July 12, 19492,619,035 Lewis Nov. 25, 1952 2,796,834 McCalfrey June 25, 1957 FOREIGNPATENTS 747,878 Great Britain Apr. 18, 1956

